In the die cutting of generally flat sheets of material such as sheets of cardboard box material to produce sheets of predetermined configuration and/or for scoring the sheets to provide for folding on predetermined lines, it is desirable to use a roll-type die cutting machine, particularly when a high volume of sheets must be die cut. One form of rotary die cutting machine is disclosed in U.S. Pat. No. 3,588,095, wherein sheets are successively fed from the bottom of a stack between a set of parallel rolls one of which carries the die cutting knives or blades and the other of which carries a resilient pad or mat which is engaged by the blades on the die cutting roll.
The sheets are successively fed from the bottom of the stack by a reciprocating feed plate which forces the bottom sheet of the stack into a nip defined by a pair of parallel feed rolls disposed adjacent the die cutting and back-up rolls. All of the rolls are driven by an electric motor which also drives a crank connected by a link member to reciprocate the feed plate. The feed plate is also adjustable relative to the link member when the machine is stopped in order to adjust the leading edge of the feed plate according to the size of the sheets within the stack and to change the timing when the bottom sheet is advanced into the feed rolls to arrive at the desired registration between each sheet and the die cutting blades on the die cutting roll.
In order to prevent repetitive engagement of the die cutting blades with the resilient mat during each revolution of the rolls, a hydraulic cylinder has been used to reciprocate the back-up rolls slowly, for example, as disclosed U.S. Pat. No. 3,272,047. While such reciprocation of the back-up roll is helpful in preventing repetitive engagement of the blades on the die cutting roll with the mat during each revolution of the rolls, the reciprocation of the back-up roll does not avoid repetitive engagement of the blades on the die cutting roll with the mat at relatively close periodic intervals.